Industrial grinders, in general, and horizontally fed hammer mills, in particular, are used to process materials into smaller pieces. Large industrial grinders are used for grinding wood, such as wood from storm debris, land clearing, building demolition or other sources into chips which can be disposed of or used for mulch. Such grinders are also used for grinding old tires and solid waste. A common configuration of an industrial grinder is a horizontal mill with an end feed system that includes a conveyor, a press wheel, a wheel pivot mount, and a hammer mill box or frame intended to enclose the hammer mill during the feeding process. The conveyor is normally a slide chute, drag chains, or a conveyor belt or chain used to move material from the input feed chute into the enclosed hammer mill assembly. In a horizontal hammer mill, the feed material is typically fed into the hammer mill by a conveyor belt or chain.
Hammer mills may utilize a feed roller that rides on or presses down against the feed material. The feed roller generally comprises a rotating drum positioned on the infeed side of the hammer mill above the inlet horizontal conveyor. The feed roller may be a passive roller wheel that travels over the top of the feed material to hold the material down or compact it before entering the hammer mill. Alternatively, the feed roller may be power driven—i.e. the roller turns and pushes the feed material into the hammer mill assembly for processing. In order to facilitate the movement of the feed roller over the top of the material, the feed roller assembly may allow for vertical deflection to allow the roller to travel vertically over vertical variations of the feed material. Commonly, this vertical deflection of the feed roller is achieved by a pivot pin, hinge or sliding mechanism located on top, in front, or behind the hammer mill frame on the feed roller assembly. In some applications, the feed roller is biased downwardly by hydraulics or other means in order to hold the material down as it is being ground. A feed roller may be used on material entering the hammer mill or material exiting the hammer mill.
The hammers in a hammer mill are typically heavy and require frequent maintenance. Hammers for some hammer mills may weigh over 100 pounds each. The hammers are typically bolted to a cylindrical body of the hammer mill. Generally, the hammers have hammer tips and other wear parts bolted or pinned to the hammer. Additionally, a screen is located below the hammer mill and typically made of thick steel with variously sized holes. The hammer mill grinds against the screen grates as part of the grinding process. The hammer mill assembly and screens require frequent maintenance including replacing worn hammer tips, wear parts and screens due to wear and size changes. In a horizontally fed hammer mill, the feed roller must be moved away from the hammer mill so that the parts can be regularly replaced or maintained.
The configuration of enclosing the hammer mill and incorporating input and output feeder systems and rollers has presented challenges associated with maintaining the hammer mill assembly as described above. Typically, a pair of hydraulic cylinders lift the feed roller upward from the hammer mill to provide access for maintenance and repair of the hammer mill. Past attempts to hinge tilt the top of the mill box and feed roller assembly include tilting the feed roller either forward or backward, relative to the direction of the conveyor, to gain access to the hammer mill assembly.
A problem with such an arrangement is that the feed roller has a tendency to fall back down into place adjacent the hammer mill. Hammer mills of this design may typically have a safety lock or other device that would prevent the feed roller from coming down into its working position. However, it is often a problem that a worker may not engage the safety devices, the safety devices fail during use or the safety devices no longer operate. For all of these reasons, a problem with horizontally fed hammer mills is that the feed roller has a tendency to come down into its working position and can injure or crush a worker who is in a position to maintain the hammer mill. U.S. Published Patent Application 2004/0135018 by Bonner attempts to correct this problem by moving the center of gravity of the feed roller assembly such that when the feed roller assembly has been lifted into the open position by the lifting mechanism, the center of gravity of the feed roller assembly is on the side of the assembly that pivots away from the hammer mill. This results in the feed roller assembly tending to fall to the open position rather than towards the hammer mill and the closed position. Thus, if the safety devices or lifting mechanism fail, the feed roller assembly would not fall towards the worker or the hammer mill.
However, the forward or backward tilting feed rollers of the prior art provide only limited worker access to the hammer mill assembly. Because the feed roller tilts forward or backward on the conveyor, a worker's access and area of work is limited. Additionally, feed roller units that tilt up on the engine side of the hammer mill create an additional hazard in that dust and debris that may have built up on the roller assembly dumps into the engine area when the assembly is tilted.
What is needed to address the problems of the prior art is a hinged feed roller assembly for horizontal end feed style grinders or hammer mills that allow greater worker access to the hammer mill assembly and screens while not subjecting the worker to risk of injury due to failure of the lifting mechanism or safety devices.